Radio link transmission is a synchronous communication. Through the use of frame offsets, the serving radio network controller (S-RNC) establishes a time line for transmitted data relative to the broadcast channel (BCH), which serves as a time reference. The connection frame number (CFN) is not transmitted over the air interface. Instead, it is mapped by L1 (the air interface) to the system frame number (SFN), by using the L1 frame counter and a frame offset. The SFN is broadcast by L1 in the BCH. Data frames must be available at L1 on time for transmission at a specific CFN. This requires accurate and coordinated timing of each network node and transmission link on the data path there between. It is desirable to provide a system and method for handling downlink data transmission and for optimally sizing data buffers that are related to the transmission synchronization.